JR,

That picture of his Hong Kong Main shows a shelve. JR, a shelve fitted
main is a Free Footed Main. The shelve is ONLY to prevent air from
creating a vortex,

Is you look at that picture you will see that the airfoil shape carries
to the very bottom of the sail, then the shelve (which is open) carries
straight across to the boom. Just like a "shelve" the reason for its'
name.

JR, think of your own main REEFED. You have a free footed sail with the
access sail folded and loosely tied to the boom . It should never be
tied tight enough for support.